Apparatus for burning solid fuel



June 11, 1957 w MaoD. URQUHART APPARATUS FOR BURNING $01.10 FUEL 2Sheets-Sheet 1 Filed Feb. 25, 1953 INVENTOR Mum/w M P'Qll/MRT ATTORNEYJune 11, 1957 w. Ma D. URQUHART 7 APPARATUS FOR BURNING SOLID FUEL.

Filed Feb. 25, 1953 2 Shee ts-Sheet 2 I INVENTOR Mum/MAI. l/RQl/AWATATTORNEY United States Patent 2,795,200 APPARATUS FOR BURNING SOLID FUELWilliam MacDonald Urquhart, Glasgow, Scotland asslgnor to The Babcock &Wilcox Company, New fork, N. Y., a corporation of New Jersey ApplicationFebruary 25,1953, Serial No. 338,797

Claims priority, application Great Britain February 27, 1952 The presentinvention relates to combustion apparatus, and more particularlytospreader stoker fired furnaces wherein atravelling grate moves fromfront to rear of the lower portion of the furnace Inspeader stoker firedfurnaces of the type described, some of the fuel particles introducedinto the furnace have flight trajectories whereby the fuel is thrown tothe rear portion of the furnace: where they are discharged in anunburned condition with the fuel ashes. This condition can occur witheither mechanical or pneumatic types of spreader stokers, and results inan undesirably high carbon loss.

In accordance with this invention means are provided in the rear portionof the furnace to intercept a large portion of-the solid fuel particlesthrown to the rear of the furnace, and to return the particles to thefurnace where they are burned-r As hereinafter described, an uprightshield is provided adjacent the rear wall of the furnace with the lowerend thereof spaced above the upper surface of the burning. fuelbed andthe included fuel ash. The shield intercepts theparticles thrown towardthe rear wall of the furnace in flight trajectory abovethe fuel bed.Additionally, an inwardly vprojecting. ledge is supported onthelowerportion of the shield so that the fuel particles that-d not-reboundfrom-the shield tofallon the furnace grate collect on theledge fromwhichthey are blown forwardly into the furnace by fluid jets.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming. apart. of this specification For a better understanding of the invention,its operating advantages and specificobjectsattained by its use,.reference should be had tothe accompanying drawings and descriptivematter in: which I haveillustrated and described preferred embodimentsofmy invention Of the drawings:

Fig. l is an elevation in longitudinal section through thelowerportionof a spreader. stoker firedfurnaceconstructed and arrangedaccording'tothe presentinvent-ion;

FigHZ-is-apIanof part of the furnace coalsupply mechanism, includingtwo-adjacent spreader units taken on the line- 2-2 ofs'Figr 1;.

Fig", 3 is-apart ofvFigr 1' to a larger scale; including means adjacentthe lower end ofwthe furnace rear wall arranged for redirecting coalforwardly within the-furna'ce,

and a Fig. t is a forward elevation of the coal' redirecting meansshown.in.Fig. 3. 7

Referring to the drawings,.the furnace has a. front wall I and" a rearwall' 2 at the ends'ofla combustion space 3 above a travelling grate 4ofthe chain grate type arranged so thatlits'upp'errunmoves'r'ea'rwardly.

In front off'a'nd extending laterally of the front: wall 1 is arranged ahopper 5', into which deal is led from an overheadhunkerp through a"traversing chute 7.' At the bottomof'thehop'per and arranged side bysidein" arow extending laterally ofthe furnace are a number of feeders 8operating on' the e'ndless' conveying surface principle.

The feeders are arranged during operation to remove coal rearwardly fromthe hopper. Suitably all the feeders are driven at the same speed bycommon driving means. The amounts of coal fed by the feeders can beadjusted individually by raising or lowering guillotine doors 9positioned above the rear ends of the feeders and slidable within therear wall 10, which is a double wall of the hopper.

Coal is prevented from falling in front of the feeders by plates 11 andfrom falling between the feeders by ridged structures 12. v

The coal from the rear ends of the feeders is arranged to fall ontoacommon chute '13 sloping downwardly and rearwardly. At thebott'om ofthe chute behind each feeder is a plate I4 of a respective spreader unit15, which is arranged to receive the coal falling from the rear end ofthe feeder. The chute is provided with structures 16 of refractorybetween adjacent spreader units, which are formedwithsloping surfaces I7normal to the main surface of the chute and adapted to direct coalfalling thereon towards the nearmost spreader unit. The side surfaces 18of the structures 16 act to confine the falling coal to paths leadingthem to the spreader units.

Adjacent each spreader unit plate 14 the lowermost part of the chute isformed by a metal block 19. The surface of the chute above these blocks,between the refractory structures 16 and above the-level thereof, isformed by the surfaces of refractory bricks 20.

I A fixed. scraper, plate 21- is provided adjacent the rear of eachfeeder to insure the falling from the feeder conveying surface of coalthat might otherwise adhere thereto. A screen 22' projecting downwardlyand forwardly from the furnace front Wall 1 near the bottom thereof isprovided for intercepting radiation from the furnace that might damagemechanical parts of the feeders.

In' the embodiment of the invention shownin the draw ings,.center linesof adjacent spreader units are 1 9 /2 apart. Each spreader unit plate 14is bolted to the block 19 and has a shelf 23 extending horizontally andrearwardly from the bottom of the chute a distance of 5"; the rear part24 of the plate is a deflector providing a guide surface which-curvesupwardly, the curvature being cylindrical around a laterally extendingaxis distant 6" from the upper surface of the plate; the plateterminates where the slope thereof has an angle of 33 or thereabouts tothe ho izontal; The side edges 25 of the plate diverge rearwardl y,being 10 /4 apart at the front edge of-the shelf and I6" apart at therear edge of the deflector. The side edgesof the plate are furnishedwith upstanding guide Walls 26 having their upper edges horizontal andat a height of 2 /2 above the level of the shelf 235 and provided' withforward and pward extensions 27 defining the path of the c'o'al fallingover the part of the chute provided by the block 19 The spreader unit islocated so'tha't the shelf zais 12%" above the grate. v

The spreader Stoker unit also comprises a horizo'nt'ally direete'delongated orifice so formed in the block 19. The orifice is 1'0 wide anddeep with it's lower edge /2" above the plane of the shelf 23; Theorifice registers with a slot: in a duct- 32 extending adjacent thelower endsof the chute transversely of the furnace and arranged tosupplyair to all the spreader units.

The space below' much of the upper run of the grate isdividedinto-eompartments 35-40 to which undergrate air is supplied underthe control of respective dampers 3'5a l0a. The compartments extend aszones transversely of the grate and control of the respective quantitiesof air thereto permits the rates of combustion attained at differentzones to be varied to suit the character of the coal to be burned.

At there'ar end of the furnace the" contents of the grate are ledbeneath an arch 45- at the bottomof the furnace 3 rear wall 2, beforebeing removed from the grate. by the usual ash bars 46 at the rear endof the grate. .The front surface of the rear wall 2 is extendedvertically downwardly in front of the arch 45 by the front surface of ashield 47 comprising refractory blocks 48 supported by a row side byside across thewidth' of the furnace of backing plates 49, which have attheirlower edges horizontal forwardly extending projections 50 beneaththe lowest row of blocks 48. .Each backing plate is bolted to downwardprojections 51 ofapair of respectiye supporting blocks 52.: The rearwall 2 and the arch 45 contain cooling tubes 53, and the supportingblocks 52 are clamped between respective adjacent pairs thereof in thearch 45.. V

Extending horizontally and laterally of thefurnace and immediatelybeneath the projections 50 are sections of pipe 54 which have theircenter lines at a distance of l" 1" above the main level of the uppersurface .of the grate. To each pipe section is welded a ledge 55;1" wideprojecting forwardly of the plane of the front surface. of the shield 47and in a slightly upward direction, and above the ledge 55 the pipesection 54 is slotted to form an orifice 56, deep, adapted when the pipesection is supplied with air under pressure to project an air jetsweeping over the upper surface of the ledge in a forward and slightlyupward direction.

The supporting blocks'which support a backing plate 47 support also thecorresponding pipe sectionthrough respective supporting bars 57.

The pipe sections are supplied with air under pressure through pipeconnections 58 from a common supply line (not shown). A

The furnace is adapted for the production of hot gases for steamgeneration. Appropriately the gases are led across heat absorbingsurfaces (not shown) comprising steam generating tubes and steamsuperheating tubes and subsequently through an economizer.

In operation coal prepared for spreader stoker firing, e. g. crushed andcapable of passing through a /z"n'ng, is fed from the: bunker 6 throughthe traversing chute. to the hopper 5, and the feeders 8 are operated todischarge coal continuously from the hopper to the spreader units 15.Air is supplied to the duct 32 at a pressure of 12" to 18 water gauge,and after issuing from the orifices 30 continuously projectscoalrearwardly from. thespreader units. Most of the coal particles or lumpsso supplied to the furnace burn in the fuel bed on the grate 4, which issupplied with undergrate air from the compartments 35-40. The asharising from the combustion of the coal on the grate is discharged atthe rear of the grate.

When the coal particles or lumps areacteduponby the currents of air fromthe orifices 30, they undergo rearward accelerations. During suchaccelerations the shelf 23 prevents the coal as a whole from falling.The shelves. are horizontal, and the acceleration ofa particle or lumpwhile it is over a shelf is larger than if the shelf surfaces weredirected rearwardly and upwardly. The deflector 24 at the end of theshelf 23 deflects the :relatively fast moving lump or particle so thatit leaves the spreader unit in a path having an upward inclination tothe horizontal, the angle of which will generally be relatively large.By reason of the large angles to the horizontal and the high speeds atwhich the coal lumps or particles leave the spreader units, the coalparticles or lumps destined to burn out on the grate tend to havetrajectories which carry them large distances rearwardly before theyreach the fuel bed on the grate. It is found that in this way coal lumpsor particles can be distributed over an area which is relatively greatfrom front to rear, so that the furnace can have a deep combustionspace. The currents of air from the orifices 30 fan out to a certainextent laterally, while moreover adjacent coal particles or lumps oneach spreader unit plate 14 tend to be blown apart. Coal lumpsandparticles are, therefore, dis- 4 tributed also to each side of eachspreader unit at the rear thereof. 1

The air from the orifices 30 and those coal particles or lumps destinedto fall on the fuel bed on the grate travel at least initially in.thesame general direction with l the air sweeping past such lumps orparticles. The lumps or particles are, therefore, scrubbed by the air sothat ample oxygen for rapid ignition and combustion of such particlesor, lumps is, available.

The larger lumps of coal, inasmuchas they have a smaller ratio ofsurface area to weight tend to be less greatly acceleratedby the airfrom the orifices 30 and less sustained by the mass of gases risinggenerally up-. wardly from the fuel bed on the grate, and consequentlythey tend to fall in greater. proportion towards the front end of thefuel bed on the grate. Larger lumps require a longer time for theircombustion than smaller lumps or particles, and this longer time theyreceive because the upper run of the grate moves rearwardly. The lumpsor particles falling near the rear of the fuel bed on the grate tend tobe much as are more greatly accelerated by the air currents from theorifices and more greatly sustained by the gas mass rising generallyupwardly from the fuel bed, i. e. they are generally the smaller lumpsor particles; consequently although a less time is available to thern'for combustion in the fuel. bed before they are dischar'gedfrom thegrate, they will be generally burnt out on the grate before they reachthe ash bars 46, since they require only a shorter time to burn.

The shield 47 presents to the combustion space a surface from which coalrebounds onto the grate in a forward directionyor which leads to theledges 55, many coal lumps or particles fallingfrom the rear wall :2 andfrom the shield itself. The pipe sections 54 are supplied with air underthe same pressure and suitably from the same source as that for the duct32. From the ledges 55 air discharged forwardly through the orifices 56projects the coal lumps or particles. -The coal lumps or particles whichimpinge onto. the shield at the end of their trajectories from thespreader units might not, if the shield were absent and they fell on thegrate, have time to burn out before being carried by the grate to theash bars 46, but by virtue of their redelivery in a forward direction sothat they fall onto the fuel bed on the grate infront of the plane ofthe rear wall 2 sutficient time is given to such lumps or particles tomake possible the completion of their combustion in the furnace.Moreover, the shield 47 reduces the possibility of particles or lumps inthe rain of coal projected rearwardly from the spreader units frompursuing trajectories which would carry them onto or beyond the ash bars46; at the same time the shield 47 constrains air flowing upwardlythrough the grate below the rear arch 45 to flow in a forward directionabove the grate and through the relatively narrow opening between thepipe sections 54 and the fuel bed on the grate, and this movement of airand gases is adapted ,to shorten the trajectories of lumps or particleswhich might otherwise fall too near the end of the grate- I have foundthat in the apparatus described most grades of coal adapted for spreaderstoker firing may be satisfactorily 'spread onto' grates for carryingfuel beds having lengths of from 14 to 20 feet.

The amount of air delivered to the furnace through the orifices 56 isonly a small fraction of the total air supplied. The amount of airsupplied. by the orifices 30 is greater, but to provide. it requires aminimum of auxiliary power, for although the air is admitted through theorifices 30 with a velocity sufiicient to achieve a satis-, factorydistribution of fuel by the. spreader units 15 over the grate, theaggregate area of the orifices 30 is limited. It is found that theair-quantity is substantially less than the normal requirements foroverfire air, so that no inefficiency arises by the presence of anexcessive proportion of excess air in the gases leaving the furnace.Overfire air: that may be required in addition to that from the orifices30 is provided through suitable secondary air nozzles. The high velocityof the air from the orifices 30 is a factor causing an advantageousdegree of turbulence in the gas mass rising from the fuel bed, and thuspromoting complete combustion. The pressure of air required in the duct32 is not, however, greater than that readily obtainable from a singlestage fan.

The advantages of e. g. unrestricted ignition of the coal, flexibilityin following load fluctuations, little tendency to form large clinkers,facility of burning highly swelling coals, and other advantagesassociated with spreader stoker firing are achieved in the furnacedescribed.

Certain methods and apparatus associated with the pneumatic projectionof fuel rearwardly into the furnace are disclosed and claimed in acopending application filed February 25, 1953, Serial No. 338,812 inwhich I have joined John M. Miller and Donald M. McLaren as coinventors.

While in accordance with the provisions of the statutes I haveillustrated and described herein the best form of the invention nowknown to me, those skilled in the art will understand that changes maybe made in the form of the apparatus disclosed without departing fromthe spirit of the invention covered by my claims, and that certainfeatures of my invention may sometimes be used to advantage without acorresponding use of other features.

What is claimed is:

1. Combustion apparatus including a furnace having a spreader stokeradapted to distribute solid fuel transversely of said furnace, a movinggrate in the lower portion of said furnace, the upper surface of saidgrate moving from front to rear of the furnace, an arch overlying therearward portion of said moving grate, ledge means positioned adjacentsaid rear arch and above said grate intercepting fuel particlesdischarged by said spreader stoker with a flight trajectory above thegrate, and nozzle means constituting continuous transversely elongatedslots positioned and arranged to project fuel particles collected onsaid ledge means toward the front of said furnace.

2. Combustion apparatus including a furnace having a spreader stokeradapted to distribute crushed solid fuel from front to rear of saidfurnace, a moving grate disposed in the lower portion of said furnace,the upper surface of said grate moving from front to rear of thefurnace, means for passing combustion air upwardly through said grate,an arch overlying the rearward portion of said moving grate, and meansadjacent the rearward portion of said grate to intercept particles ofsolid fuel and to project said particles forwardly in said furnacecomprising,-an upright shield having its lower end spaced above saidgrate, a ledge supported on the lower portion of said shield andextending inwardly of said furnace, and fluid jet means positioned andarranged to project fuel particles collected on said ledge toward thefront of said furnace.

3. Combustion apparatus according to claim 2, Wherein the distributionof crushed solid fuel is accomplished by jets of combustion air.

4. Combustion apparatus according to claim 2, wherein said fluid jetmeans comprises a plurality of combustion air streams disposed todischarge in a generally horizontal direction across said ledge.

References Cited in the file of this patent UNITED STATES PATENTS1,393,826 Potter Oct. 18, 1921 1,532,103 Kraemer Mar. 31, 1925 1,714,678Kreisinger May 28, 1929 2,302,173 Beers Nov. 17, 1942 2,386,336 MosshartOct. 9, 1945 2,483,728 Glaeser Oct. 4, 1949 FOREIGN PATENTS 365,354Great Britain Jan. 21, 1932 647,417 Germany July 3, 1937

